lo g 2 ( 2 x 2 ) × lo g 4 ( 1 6 x ) = lo g 4 x 3
If a 1 , a 2 , . . . a n are all the real roots of the above equation, then find the value of n a 1 + a 2 + . . . + a n
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Why did we reject 2 − 2 / 5 ?
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Because it will make the R.H.S. a negative, which is impossible in case of real numbers.
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But isn't − 5 2 in the range of lo g 2 ?
Thank you.
I dont think we should reject as square root a quadratic equation will get you positive and negative roots...
Similar method as Parth Lohomi but then I initially accepted both roots. Then I just guessed that the non-integral root should be rejected then presto! Anyway thank you Sandeep Bhardwaj for enlightening me on why that root should be rejected!! :)
Can someone tell me why did we have to ignore the (0.5)^0.4 part? Sandeep Bhardwaj sir
Root function always has positive range so the rhs in the origonal equation must be a positive number.
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The given equation can be expressed as
( 1 + 2 lo g 2 x ) ( 2 + 2 lo g 2 x ) = 2 3 lo g 2 x
Let lo g 2 x = m ,then
( 1 + 2 m ) ( 2 + 2 m ) = 2 3 m
( 1 + 2 m ) ( 2 + 2 m ) = 4 9 m 2
2 + 2 9 m = 4 5 m 2
5 m 2 − 1 8 m − 8 = 0
( m − 4 ) ( 5 m + 2 ) = 0
m = 4 , − 2 / 5 ⟹ x = 1 6 , 2 − 2 / 5
We reject 2 − 2 / 5 ∴ x = 1 6
Thus the answer is 1 1 6 = 1 6
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